Epoxy hardener systems based on aminomethylene-ethyleneureas

ABSTRACT

An epoxy-hardener system is provided having relatively long latency periods combined with relatively short cure times at low cure temperatures. The hardeners of the present invention are ureidoamines and their derivatives, which are chelates of ureido compounds and amines. The ureidoamines are prepared by reacting an amine with the ureido compound and aqueous formaldehyde without a catalyst. Complexes of ureidoamine hardeners with various blocking agents are prepared in the melt. The hardener is prevented from curing the epoxy by the reaction between the hardener and the blocking agent. The blocked hardener is then blended with the epoxy, usually by warming the mixture briefly at about 50-60 degrees C.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates generally to the field of epoxy hardenersand in particular to new and useful hardeners for epoxy compositions.

Epoxy resins are used extensively in industry for the production ofhighly diverse articles of manufacture from aerospace structures tosporting goods. Cured epoxies have excellent adhesive strength with avariety of substrates, good to excellent strength and toughness and goodresistance to solvents and chemicals. The best properties are obtainedfrom combinations of epoxy resins and various active hydrogen hardenerswhich produce thermosetting copolymer systems. Epoxy resins areindustrial commodities.

Epoxy hardeners are extremely diverse, including primary and secondarypolyamines, tertiary amines, polyphenols, polycarboxylic acids, cyclicanhydrides, acidic polyols and combinations of these.

Mixtures of epoxy resins and hardeners and various other modifiers,diluents, fillers, etc. are cured either at ambient temperature or atelevated temperature for a time sufficient to convert the initial liquidmixture to a solid copolymer having useful properties. This procedure isreferred to as the cure process or “curing.”

The cure temperature and cure time vary extensively depending on thechemical characteristics of the epoxy-hardener system. The liquidprepolymer mixture will gradually increase in viscosity over a period oftime at ambient temperature. Depending on the nature of themanufacturing process, the time for the viscosity of the epoxy-hardenermixture to increase to a predetermined value is referred to as the“latency period”, “pot life”,or “joint open time.” As a practicalmatter, these times determine the time available for various adhesivebonding processes involving metal or composite adherends orfiber-reinforced composite materials or the cycle times of variousthermosetting molding processes.

Increasing emphasis on reducing manufacturing costs has focusedattention on the development of epoxy-hardener systems having relativelylong latency periods combined with relatively short cure times at lowtemperatures. This combination presents some very difficult designproblems. In general, cure times and latency periods track together;increasing the latency period by changing a formulation generallyresults in an increase in the cure time. It is only by changing thechemical characteristics of the hardener system that increased latencycombined with shorter cure times can be obtained.

Polyamine hardeners give relatively short latency periods and willundergo partial curing at ambient temperature. However, properties areimproved by a postcure at a temperature above ambient. Variouscombinations of polyamines and tertiary, amines will cure at moderatetemperatures with somewhat longer latency periods and aromaticpolyamines and cyclic anhydride curing agents will provide still longerlatency periods but good properties require a postcure at relativelyhigh temperatures. New epoxy hardeners which can meet current industryrequirements are needed to provide short cures at relatively lowtemperatures combined with relatively long periods of latency.

Latent epoxy hardeners consisting of combinations of tertiary amines andacidic polyols have been described in U.S. Pat. Nos. 6,491,845 B1 and6,743,375 B2. The described tertiary amines were those which werecommercially available at the time. However, demands for increases inlatency and decreases in cure time have resulted in a search for newamine-type epoxy hardeners which can meet these new performancecriteria.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an epoxy-hardenersystems having relatively long latency periods combined with relativelyshort cure times at low temperatures.

It is a further object of the present invention to provide hardenershaving good inherent latency properties with epoxy resin and which canbe blocked efficiently by acidic materials to provide longer latencyperiods and shorter curing times.

Accordingly, hardeners for epoxy resins are provided which have thecapability of faster curing at lower temperatures than existinghardeners while simultaneously providing longer latency periods thanexisting hardeners. They are easily handled liquid materials having arange of viscosities and are made from cheap and readily availableindustrial chemicals. They have low vapor pressure at ambienttemperature, have no noxious odors and do not carbonate in air. Curingreactions with epoxy resins exhibit low exotherm and give cured productshaving exceptionally low cure shrinkage, high tensile strength and hightoughness.

The hardeners of the present invention are ureidoamines which arechelates of uriedo compounds and amines. Preferred ureido compoundsinclude ethyleneurea, propyleneurea(tetrahydro-2-pyrimidone), and1,3-dimethylurea. Preferred amines include secondary monoamines,secondary diamines, primary monoamines, mixed primary-secondary aminesor primary diamines.

All of the ureidoamine hardeners are prepared by reacting an amine witheither ethyleneurea, 1,3-dimethylurea or propyleneurea and aqueousformaldehyde without a catalyst.

Blocking agents for ureidoamine hardeners are either hydroxy acids suchas 2,2-bis(hydroxymethyl)butyric acid which reacts with the ureidoamineto create an internal acidic acylurea blocking group C(O)NC(O)N ormethylenebis(ethyleneurea) which forms a complex with an amine nitrogenatom due to the close proximity of the two carbonyl groups. Thehydroxyacid reacts with the ureidoamine in about 15 minutes at 150degrees C. while methylenebis(ethyleneurea) has only to be dissolved inthe ureidoamine at about 50-60 degrees C. A hydroxyacid can also becombined directly with a ureidoamine provided the reaction can beavoided by keeping the temperature well below the reaction temperatureof approximately 150 degrees C. The hydroxy acid which is in solution inthe hardener mixture forms a complex with the available tertiary aminenitrogen atom. The complex does not catalyze the epoxy curing reactionsbelow the activation temperature and the combination is latent.Methylenebis(ethyleneurea) is an excellent non-reactive solvent for ahydroxyacid such as 2,2-bis(hydroxymethyl)butyricacid and forms aresinous, low-melting complex at 1:1 molar ratio at about 50 degrees C.which is soluble in both the ureidoamine and the epoxy. All of thesehardener components react rapidly with the epoxy at the cure temperaturewhile providing excellent latency at ambient temperature.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Ethyleneurea(2-imidazolidone) is a relatively cheap heterocycle, m.p.133-135 degrees C. and insoluble in epoxy resins below the meltingpoint. It is a very weak base and reacts with epoxy at an impracticallylow rate. However, if a primary or secondary amine is combined with onemole ethyleneurea and one mole formaldehyde, a new compound is producedin which the nitrogen atom of the amine and the methylene bridgeconnecting this nitrogen atom to the ureido nitrogen atom combine toproduce a chelate structure in which the amine nitrogen can donateelectrons directly to the ureido oxygen atom. This nullifies theinternal electron shift on the ureido nitrogen atoms toward the carbonylgroup and activates the ureido hydrogen atoms so that they can reactwith epoxy. A wide variety of epoxy hardeners having useful propertiescan be produced by applying this principle.

In addition to ethyleneurea, two other ureido compounds,propyleneurea(tetrahydro-2-pyrimidone), m.p. 264-266 degrees C. and1,3-dimethylurea, m.p. 101-104 degrees C. are chemically equivalent.Ethyleneurea is the preferred parent compound.

There are three main types of ureidoamine compounds: The first typeconsists of the product formed by reacting 1 mole of a primary amineRNH₂ with 2 moles formaldehyde and 2 moles ethyleneurea where R containscarbon atoms and possibly oxygen atoms but does not contain any aminenitrogen atoms. This type of hardener does not have any capacity tocatalyze the epoxy-hydroxy crosslinking reactions and is an epoxymodifier and co-curative only. There are also some other hardeners whichdo not have precisely the same structure but which do not catalyze epoxycrosslinking reactions. The second type of ureidoamine hardener has thesame overall structure but the R group contains a tertiary amine orimidazole. For example, R=dialkylaminopropyl- where the alkyl is eithermethyl or ethyl; or R=imidazolylpropyl-. This type of ureidoaminehardener has both chain extension and crosslinking capabilities. Thethird type of ureidoamine has the same initial structure as the secondtype but has been condensed with a hydroxyacid such as2,2-bis(hydroxymethyl)propionicacid or 2,2-bis(hydroxymethyl)butyricacidor glycolic acid. This converts one of the terminal ureido groups to anacylurea C(O)NC(O)N which causes the tertiary amine or imidazole of theR group to bond internally to this acidic group, thereby rendering theentire molecule non-reactive at temperatures below the activationtemperature.

Hardeners Based on Aminomethylene-ethyleneureas.

The useful chemical reactions are between ethyleneurea and eithersecondary monoamines, secondary diamines, primary-monoamines, mixedprimary-secondary amines or primary diamines and formaldehyde. Any ofthese amines may contain additional tertiary amine groups, hydroxylgroups or ether groups.

Reacting ethyleneurea with two moles of a secondary monoamine RR′NH andtwo moles formaldehyde produces a catalytic epoxy hardener having noactive hydrogen atoms and four potentially active nitrogen atoms,designated by Structure I.

This material has no active hydrogens and is therefore an externalplasticizer for the polymer system. This limits the concentration torelatively low values and this material is best used as an accelerator.If only one secondary monoamine RR′NH is used, the catalytic hardener iscapable of reacting with the epoxy resin and an internal plasticizer isproduced, designated by Structure II.

Higher concentrations are practical and a wide range of latency and curerate characteristics can be obtained depending on the nature of the Rand R′ groups.

Preferably, for both Structures I and II, R and R′ are alkyl groupscontaining 1-12 carbon atoms, or R is an alkyl group containing 1-12carbon atoms and R′ is benzyl, or R is methyl or ethyl and R′ isanilino-, or R is methyl and R′ is 2-hydroxyethyl-, or R and R′ are both2-hydroxyethyl-, or R is methyl and R′ is 2-hydroxyisopropyl-, or R andR′ are both 2-hydroxyisopropyl-, or R and R′ are both3-dimethylaminopropyl-; or RR′N— represents the imino radicalbis(dimethylamino)methaneimino- (from tetramethylguanidine).

Several heterocyclic groups are also useful, in which case the RR′N—notation may represent piperidyl-, 4-methylpiperidyl-, pyrrolidyl-,1-methylpiperazinyl-, 1-imidazolyl-, 1-(2-methyl)imidazolyl-,1-(2-ethyl)imidazolyl-, 1-(2-ethyl-4-methyl)imidazolyl-, or1-benzimidazolyl-.

Secondary monoamines RR′NH useful for making the Structures I and II areas follows: a monoamine in which R and R′ are any combination of alkylgroups containing one to twelve carbon atoms; a monoamine with R beingany combination of an alkyl group containing from one to twelve carbonatoms and R′=benzyl; piperidine; 4-methylpiperidine; pyrrolidine;1-methylpiperazine; 3,3′-iminobis(N,N-dimethylpropylamine;tetramethylguanidine; N-alkylaniline where the alkyl is methyl or ethyl;imidazole; 2-methylimidazole; 2-ethylimidazole;2-ethyl-4-methylimidazole; benzimidazole; N-methylethanolamine;diethanolamine; N-methylisopropanolamine; diisopropanolamine.

A secondary diamine such as piperazine can react with two molesformaldehyde and two moles ethyleneurea to produce Structure III.Piperazine is the only commercially available secondary diamine at areasonable price.

The advantage of this structure over that of the original piperazine isthat this material has good latency and is therefore useful as amodifier to alter the solvent power of the epoxy, increase viscosity andincrease the hydroxyl group concentration. It is not a catalytichardener.

One or two moles of a primary monoamine RNH₂ can react with one or twomoles formaldehyde and one mole ethyleneurea to produce a wide varietyof secondary amines. The monosubstituted version is shown in StructureIVa. The disubstituted version is shown in Structure IVb.

Although this class of epoxy hardeners has considerable utility, latencycan be improved by reacting Structure IVb with two additional molesethyleneurea and two moles formaldehyde, producing Structure V.

A primary monoamine RNH2 can react with two moles formaldehyde and twomoles ethyleneurea to produce the Structure VI.

If R does not contain any additional nitrogen atoms, the single centraltertiary nitrogen atom is shared between the two carbonyl groups but issterically hindered and the material is essentially devoid of catalyticactivity. However it is capable of reacting with epoxy at either ambienttemperature or elevated temperature depending on the basicity of theamine RN and can be used to modify the epoxy resin, either by adding itto the hardener package or by pre-reacting it with the epoxy. When themodified epoxy is subsequently cured, the increased hydroxylconcentration increases the cure rate markedly. The fastest cures areobtained by pre-reacting this difunctional modifier with the epoxy.

If R contains a tertiary amine, the hardener molecule is both a chainextender and a catalytic hardener Examples of two primary/tertiaryamines are N,N-dialkyl-1,3-propanediamine where alkyl is methyl or ethyland 1-(3-aminopropyl)imidazole.

Preferably, for Structures IV, V, and VI, R is an alkyl containing from1 to 12 carbon atoms, allyl-, benzyl-, 2-hydroxyethyl-,2-hydroxyisopropyl-, 3-hydroxy-1-propyl-, 3-ethoxypropyl-,3-propoxypropyl-, 3-isopropoxypropyl-, 2-(2-hydroxyethoxy)ethyl-,3-(dimethylamino)propyl-, 3-(diethylamino)propyl-, or3-(1-imidazolyl)propyl-.

For Structures V and VI, RN═ may be a heterocyclic group in which Rrepresents cyclohexyl-; 3-(pyridyl)methyl-; 2-pyridyl-;2,4-diethyl-N-anilino-; 2,6-diethyl-N-anilino-; or 2-pyrimidyl-.

Primary monoamines useful in the preparation of Structures IV, V and VIare as follows: RNH2 is an alkyl monoamine containing from one to twelvecarbon atoms in the alkyl group; allylamine; benzylamine; ethanolamine;isopropanolamine; 3-amino-1-propanol; 3-ethoxypropylamine;3-propoxypropylamine; 3-isopropoxypropylamine; 2-(2-aminoethoxy)ethanol;3-dimethylamino)propylamine, 3-(diethylamino)propylamine;1-(3-aminopropyl)imidazole; cyclohexylamine; 3-(aminomethyl)pyridine;2-aminopyridine; 2,4-diethylaniline; 2,6-diethylaniline;2-aminopyrimidine.

Oligomers of higher molecular weight based on Structure VI can beproduced by increasing the amount of formaldehyde. For example,Structure VI contains 2 moles ethyleneurea, 2 moles formaldehyde and 1mole of a primary monoamine. The dimer of VI would be formed from 4moles ethyleneurea, 5 moles formaldehyde and 2 moles of a primarymonoamine. as shown below as Structure VIa.

Another possibility is 4 moles of ethyleneurea, 4 moles formaldehyde and1 mole of a primary monoamine, resulting in the oligomer shown below asStructure VIb.

Such higher molecular weight materials may be useful in improving curedproperties and in providing extended latency with tertiary amine typecatalytic hardeners. However, it should be expected that cure times willincrease with the use of these higher molecular weight materials.

A mixed primary-secondary amine HNR—X—NH2 can be made to react with twomoles ethyleneurea and two moles formaldehyde, producing the StructureVII.

While this structure is superficially similar to Structures III and IV,the unreacted hydrogen atom can be employed to attach an additionalamine-functional molecule such as imidazole near the center of themolecule which can result in a latent hardener due to the sterichindrance of the added amine group. The backbone of the molecule is alsomore flexible based on the choice of the connecting group X which can beused to increase flexibility and toughness of the cured polymer.

For Structure VII, X is a connecting group which can be ethylene forexample. R is hydroxyethyl or aminoethyl for example.

Mixed primary-secondary amines which are useful in the preparation ofStructure VII are N-(2-hydroxyethyl)ethylenediamine anddiethylenetriamine. Although diethylenetriamine has five activehydrogens, the indicated structure has been successfully prepared usingthe procedure to be described subsequently. The unreacted aminehydrogens are not epoxy-reactive and can be used to attach side groupssuch as tertiary amines or imidazole.

A primary diamine H₂NXNH₂ can be reacted with two moles formaldehyde andtwo moles ethyleneurea provided the process is carefully controlled toprevent multiple substitution of the amine groups by formaldehyde. Theresult is shown in Structure VIII.

Because Structure VIII contains two unreacted amine hydrogen atoms, oneor both of these can be used to attach additional amine groups HNRR′ oradditional ethyleneurea groups to the molecule via theamine-formaldehyde reaction, forming Structures IX and X. In order toobtain good control over the structure of these molecules, structure IXis obtained from structure VIII by a sequential reaction rather than allat once.

For Structures VIII, IX, and X, connecting group X is for example alkyl,ethylene as in ethylenediamine, or polyoxypropylene as inpoly(propyleneglycol)bis(2-aminopropylether), or hexamethylene or2,2,4-trimethylhexamethylene. Cycloaliphatic and aromatic connectinggroups are also possible. For example, X can also be cyclohexyl orbenzene.

Preferably, for Structure IX, R and R′ are alkyl groups containing 1-12carbon; atoms, or R is an alkyl group containing 1-12 carbon atoms andR′ is benzyl, or R is methyl or ethyl and R′ is anilino-, or R is methyland R′ is 2-hydroxyethyl-, or R and R′ are both 2-hydroxyethyl-, or R ismethyl and R′ is 2-hydroxyisopropyl-, or R and R′ are both2-hydroxyisopropyl- or R and R′ are both 3-dimethylaminopropyl- or RR′N—represents the imino radical bis(dimethylamino)methaneimino- (fromtetramethylguanidine).

Several heterocyclic groups are also useful, in which case the RR′N—notation may represent piperidyl-, 4-methylpiperidyl-, pyrrolidyl-,1-methylpiperazinyl-, 1-imidazolyl-, 1-(2-methyl) imidazolyl-,1-(2-ethyl)imidazolyl-, 1-(2-ethyl-4-methyl)imidazolyl-, or1-benzimidazolyl-.

Secondary monoamines RR′NH useful for making the Structure IX are asfollows: a monoamine in which R and R′ are any combination of alkylgroups containing one to twelve carbon atoms; a monoamine with R beingany combination of an alkyl group containing from one to twelve carbonatoms and R′=benzyl; piperidine; 4-methylpiperidine; pyrrolidine;1-methylpiperazine; tetramethylguanidine; N-alkylaniline where the alkylis methyl or ethyl; imidazole; 2-methylimidazole; 2-ethylimidazole;2-ethyl-4-methylimidazole; benzimidazole; N-methylethanolamine;diethanolamine; N-methylisopropanolamine; diisopropanolamine;3,3′-iminobis(N,N-dimethylpropylamine).

Primary diamines useful in the preparation of Structures VIII and IX, aswell as the tetra(ethyleneurea) product Structure X, are as follows:Ethylenediamine; 1,3-propanediamine; 1,3-diaminopentane;2-methyl-1,5-pentanediamine; 1,6-diaminohexane;2,2,4-trimethyl-1,6-hexanediamine;poly(propyleneglycol)bis(2-aminopropylether);1,3-bis(aminomethyl)cyclohexane; bis(p-aminocyclohexyl)methane;isophoronediamine; m-xylylenediamine; 1,2-phenylenediamine;1,4-phenylenediamine; 4,4′-methylenedianiline; 2,6-diaminopyridine.

Formation of Latent Hardeners.

The ureido NH groups of the aminomethylene-ethyleneureas reactvigorously with anhydrides and will also condense with carboxylic acidswhen heated. This characteristic can be used to modify the structure andincrease latency. The condensation reaction of Structure VI with either2,2-bis(hydroxymethyl)propionicacid or 2,2-bis(hydroxymethyl)butyricacidor glycolic acid produces an acylurea group C(O)NC(O)N, which is acidic,shown in Structure XI. That is, the resulting derivative in Structure XIis an acyl derivative of Structure VI. Nitrogen atoms present in the Rgroup will be bonded internally to this acidic group and will becomeunavailable to catalyze either the reaction of the remaining ureido NHgroup with epoxy or the epoxy-hydroxy reaction until the temperaturereaches the activation temperature. All of the above hydroxy acids arevery effective in extending latency and will condense with Structure V1at about 150-180 degrees C. in 15 minutes, giving products which areamber, solid resins.

The R group is either dialkylaminopropyl- or imidazolylpropyl-. Latencyperiods of about one week and cure times of about three hours at 75degrees C. can be obtained with dialkylaminopropylamine whileaminopropylimidazole leads to about a one month latency period with acure time of about one hour at 120 degrees C.

The same method may be used to convert iminomethylene-ethyleneurea,Structure IVa, into a latent catalytic hardener. The R group is againeither dialkylaminopropyl- or imidazolylpropyl-. Reacting themono-iminomethylene-ethyleneurea with one mole2,2-bis(hydroxymethyl)butyric acid converts the imino group into atertiary amide which is weakly acidic and which provides a bonding sitefor the tertiary amino nitrogen atom in the R group, shown in StructureXII below.

A second approach to improving latency is to combine a hardener such asshown in Structure VI which contains a tertiary amine or imidazole inthe R group with a blocking agent which will bond to this tertiary aminenitrogen atom at ambient temperature but release it at the curetemperature, which will preferably be a low temperature such as about 75degrees C. This delicate task is performed well by the compoundmethylenebis(ethyleneurea) which has a structure which places the twocarbonyl groups close together, forming an attractive bonding site for anitrogen atom. While this material is not commercially available,urea-formaldehyde technology is well established and preparation issimple using 1 pph of a basic catalyst such as dimethylamine which neednot be removed from the product. This material is mixed with the otherhardener components at a ratio of one mole per nitrogen atom to beblocked. It is fully compatible and cures an epoxy in about 30 minutesat 75 degrees C. when base catalyzed as indicated. Latency periods areabout 8 hours.

A hydroxyacid can also be combined directly with a ureidoamine providedthe condensation reaction can be avoided by keeping the mixingtemperature well below the reaction temperature of approximately 150degrees C. The hydroxy acid which is in solution in the hardener mixtureforms a complex with the available tertiary amine nitrogen atom. Thecomplex does not catalyze the epoxy curing reactions below theactivation temperature and the combination is latent.Methylenebis(ethyleneurea) is an excellent non-reactive solvent for ahydroxyacid such as 2,2-bis(hydroxymethyl)butyricacid and forms aresinous, low-melting complex at 1:1 molar ratio at about 50 degrees C.which is soluble in both the ureidoamine and the epoxy. The use of thisureido compound greatly facilitates the mixing of the various hardenercomponents at a low temperature. All of these hardener components reactrapidly with the epoxy at the cure temperature while providing excellentlatency at ambient temperature.

Preparation of Ureidoamine Hardeners.

The same process is used to prepare all of the ureidoamine compoundsdisclosed. While the process is a simple one, the temperature conditionsare exacting and must be strictly adhered to. Bench scale preparationrequires a reaction flask, condenser, stir bar, stirring hot plate,water/ice bath and electronic thermometer with a stainless steel probe.An electronic thermometer is required because it has a fast response anddoes not require a stem correction.

The reaction involves an amine, water, formaldehyde and ethyleneurea.The order of addition is amine first, then water of dilution, thenaqueous formaldehyde, then ethyleneurea.

The amine is first weighed into the flask and distilled water is added,the weight of which is equal to the weight of ethyleneurea which is tobe added at a later step. The purpose of adding water at this step is toallow the exotherm which occurs when the amine reacts with water todissipate before adding aqueous formaldehyde, thereby minimizing thetemperature rise during formaldehyde addition. The extra mass of wateralso helps to minimize the temperature rise. The stir bar is added andthe flask is clamped into a cold bath of water and ice and stirred untilthe temperature has fallen to 5-10 degrees C. The required weight offormaldehyde is weighed into a beaker and slow addition to the flask isbegun using a dropper while closely monitoring the temperature of themixture. Formaldehyde addition is stopped before the temperature reaches15 degrees C. and the temperature is allowed to fall back to 5-10degrees C. before adding more formaldehyde.

The temperature must not rise above 15 degrees C. during formaldehydeaddition. The methylolamine which is formed at this stage associatesthrough the hydroxy groups which protects the unreacted amine hydrogensuntil the temperature reaches about 30-35 degrees C. at which point thecomplex dissociates, the methylols condense with amine and the processfails.

When the formaldehyde addition has been completed, the beaker is rinsedwith a little distilled water and added to the flask. The requiredamount of ethyleneurea is now weighed out, the stirrer speed increasedto medium high and the ethyleneurea added to the flask all at oncethrough a plastic funnel. The temperature will immediately fall to about0-5 degrees C. as the ethyleneurea dissolves. The ice should now beremoved from the cold bath, the water level in the bath brought up tothe level of the contents of the flask, the condenser attached andheating begun at a rate which brings the temperature up to 90 degrees C.in about half an hour. All of the ethyleneurea will be in solution bythe time the bath temperature reaches about 35-40 degrees C. The mixtureshould be heated for 2 hours at 90 degrees C. at the end of which it canbe poured into an evaporating dish and dried to constant weight at aliquid temperature of 60-70 degrees C. The products of this reaction aretypically colorless to pale amber viscous liquids or amorphoussemi-solids of little or no odor. They do not carbonate in air and aresoluble in epoxy resins.

EXAMPLES

In the examples given below, the notation A/B denotes a chemicalreaction between the two chemical compounds A and B, using formaldehydeas appropriate. The epoxy resin was Epon828 in all cases.

Example 1 2EU/DEAPA

This hardener was prepared by reacting 2 moles ethyleneurea with onemole DEAPA [3-(diethylamino)propylamine] and 2 moles formaldehydeaccording to the procedure previously described and is an example ofStructure VI. It is both a chain extender and a catalytic hardener. Thephysical form of this material was a highly viscous resin at ambienttemperature. The recommended minimum concentration in Epon828 is 7.5phr. 20 phr of this hardener (a large excess) was blended with Epon828and maintained at ambient temperature, resulting in a three-foldviscosity increase after 4 hours. The cure time was 1 hour at 75 degreesC.

Example 2 2EU/EDA

Two moles ethyleneurea and 1 mole ethylenediamine were reacted with 2moles formaldehyde according to the standard procedure giving a materialshown in Structure VIII. This hardener is capable of chain extensiononly, having no tertiary amine group and is best described as an epoxymodifier. This material was then blended with Epon828 at a concentrationof 10 phr and the mixture heated at 1,00 degrees C. for 1.5 hours,giving a product which was a medium viscosity liquid hot and highlyviscous at ambient temperature. After one month at ambient temperaturewith occasional reheats to temperatures as high as 130 degrees C., themodified epoxy was a tacky, flexible semi-solid at ambient temperature.This system has a tendency to increase viscosity slowly over extendedperiods of time but does not appear to crosslink and remains fusible.

Example 3 2EU/API Reacted with DMBA

Two moles ethyleneurea were reacted with 1 mole1-(3-aminopropyl)imidazole (API) and 2 moles formaldehyde giving amaterial as shown in Structure VI. A test sample was then prepared using7.0 phr of this hardener in Epon828. The pot life at ambient temperaturewas 4 hours. The cure time was 1.5 hours at 80 degrees C.

A second sample was then prepared using 6.0 phr of this hardener butadding one mole (2.77 phr) DMBA [2,2-bis(hydroxymethyl)butyricacid] permole 2EU/API and heating for 15 minutes at 100 degrees C. to fullydissolve the acid in the ureidoamine. 4.0 phr 2EU/EDA was then added asa solubilizer. This sample was cured in 1 hour at 120 degrees C.

The viscosity increased by 2.5 times during the first 2 days at ambienttemperature. This was due to the slow reaction of the non-catalyticepoxy modifier 2EU/EDA with the epoxy and is a “conditioning period”.The viscosity of the epoxy-hardener mixture at the end of 23 additionaldays at ambient temperature was 3.6 times the value at 4 days aftermixing. The mixture was still viscous and flowable after 30 days atambient temperature.

Example 4 2EU/API Blocked with MBEU

This sample contained 15 phr 2EU/API and 8.6 phr MBEU[methylenebis(ethyleneurea)] as blocker for the R-group imidazole asshown in Structure VI. The cure time was 35 minutes at 75 degrees C.After 12 hours at ambient temperature, the viscosity of theepoxy-hardener mixture increased by 1.7 times.

Example 5 2EU/DEAPA Blocked with DMBA.MBEU

3.4 phr DMBA [2,2-bis(hydroxymethyl)butyricacid] and 4.22 phr MBEU[methylenebis(ethyleneurea)] were heated at about 50 degrees C. for abrief period; the DMBA dissolved rapidly resulting in a clear solutionwhich was a tacky, resinous, low-melting solid at ambient temperature.7.5 phr 2EU/DEAPA was then added and blended briefly at about 50 degreesC. followed by blending with the epoxy. This mixture cured in 2¼ hoursat 75 degrees C. The viscosity of the epoxy-hardener mixture increasedby a factor of 3 after 3 days at ambient temperature.

1. A composition comprising: an epoxy resin; and a reaction product thatcontains at least one ureidoamine or a derivative thereof as a hardenerand a blocking agent for blocking said ureidoamine or derivative.
 2. Acomposition according to claim 1, wherein a ureido compound of theureidoamine is selected from the group consisting of ethyleneurea,propyleneurea, and 1,3-dimethylurea.
 3. A composition according to claim1, wherein the blocking agent is at least one hydroxy acid selected fromthe group consisting of 2,2-bis(hydroxymethyl)butyricacid,2,2-bis(hydroxymethyl)propionicacid and glycolic acid, ormethylenebis(ethyleneurea), or a combination of at least one of saidhydroxy acids and methylenebis(ethyleneurea).
 4. A composition accordingto claim 1, wherein an amine compound of the ureidoamine is selectedfrom the group consisting of primary monoamines, secondary monoamines,primary diamines, secondary diamines.
 5. A composition according toclaim 1, wherein the ureidoamine is selected from the group consistingof Structures I and II:

wherein R and R′ are any combination of alkyl groups containing one totwelve carbon atoms, or R is any combination of an alkyl groupcontaining from one to twelve carbon atoms and R′ is benzyl, or R ismethyl or ethyl and R′ is anilino-, or R is methyl and R′ is2-hydroxyethyl-, or R and R′ are both 2-hydroxyethyl-, or R is methyland R′ is 2-hydroxyisopropyl-, or R and R′ are both 2-hydroxyisopropyl-;or R and R′ are both 3-dimethylaminopropyl; or RR′N— is the iminoradical bis(dimethylamino)methaneimino-, or RR′N— is heterocyclic andselected from piperidyl-, 4-methylpiperidyl-, pyrrolidyl-,1-methylpiperazinyl-, 1-imidazolyl-, 1-(2-methyl)imidazolyl-,1-(2-ethyl)imidazolyl-, 1-(2-ethyl-4-methyl)imidazolyl-, or1-benzimidazolyl-.
 6. A composition according to claim 1, wherein theureidoamine is Structure III;


7. A composition according to claim 1, wherein the ureidoamine isselected from the group consisting of Structures IVa, IVb, V, and VI:

wherein R is an alkyl containing from 1 to 12 carbon atoms, allyl-,benzyl-, 2-hydroxyethyl-, 2-hydroxyisopropyl-, 3-hydroxy-1-propyl-,3-ethoxypropyl-, 3-propoxypropyl-, 3-isopropoxypropyl-,2-(2-hydroxyethoxy)ethyl-, 3-(dimethylamino)propyl-,3-(diethylamino)propyl-, or 3-(1-imidazolyl)propyl-; or RN═ is aheterocyclic group in which R is cyclohexyl-, 3-(pyridyl)methyl-,2-pyridyl-, 2,4-diethyl-N-anilino-, 2,6-diethyl-N-anilino-, or2-pyrimidyl-.
 8. A composition according to claim 7, wherein theureidoamine is an oligomer of Structure VI selected from the groupconsisting of Structures VIa and VIb;


9. A composition according to claim 1, wherein the ureidoamine isStructure VII

X is ethylene; and R is CH₂CH₂OH or CH₂CH₂NH₂.
 10. A compositionaccording to claim 1, wherein the ureidoamine is selected from the groupconsisting of Structures VIII and X:

wherein X is ethylene, polyoxypropylene, hexamethylene, cycloaliphatic,or aromatic.
 11. A composition according to claim 1, wherein theureidoamine is Structure IX:

wherein x is ethylene, polyoxypropylene, hexamethylene, cycloaliphatic,or aromatic; and R and R′ are alkyl groups containing 1-12 carbon atoms,or R is an alkyl group containing 1-12 carbon atoms and R′ is benzyl, orR is methyl or ethyl and R′ is anilino-, or R is methyl and R′ is2-hydroxyethyl-, or R and R′ are both 2-hydroxyethyl-, or R is methyland R′ is 2-hydroxyisopropyl-, or R and R′ are both 2hydroxyisopropyl-;or R and R′ are both N,N-dimethylaminopropyl-; or RR′N— is the iminoradical bis(dimethylamino)methaneimino-, or RR′N— is heterocyclic, inwhich case RR′N— is piperidyl-, 4-methylpiperidyl-, pyrrolidyl-,1-methylpiperazinyl-, 1-imidazolyl-, 1-(2-methyl)imidazolyl-,1-(2-ethyl)imidazolyl-, 1-(2-ethyl-4-methyl)imidazolyl-, or1-benzimidazolyl-.
 12. A composition according to claim 1, wherein theureidoamine derivative is an acyl derivative of Structure VI:

wherein R— is dialkylaminopropyl- or imidazolylpropyl, and the acylcompound is one of 2,2-bis(hydroxymethyl)propionicacid;2,2-bis(hydroxymethyl)butyricacid or glycolicacid.
 13. A compositionaccording to claim 1, wherein the ureidoamine derivative is an acylderivative of Structure IVa:

wherein R— is dialkylaminopropyl- or imidazolylpropyl- and the acylcompound is one of 2,2-bis(hydroxymethyl)propionicacid;2,2-bis(hydroxymethyl)butyricacid or glycolicacid.
 14. A blockedhardener composition for mixing with an epoxy to cure the epoxy, theblocked hardener composition comprising: a ureidoamine or a derivativethereof; and a hydroxy acid selected from the group consisting of2,2-bis(hydroxymethyl)butyricacid and2,2-bis(hydroxymethyl)propionicacid and glycolic acid, ormethylenebis(ethyleneurea), or a combination of at least one of saidhydroxy acids and methylenebis(ethyleneurea); wherein the blockedhardener is soluble in epoxy resin.
 15. A blocked hardener compositionaccording to claim 14, wherein a ureido compound of the ureidoamine isselected from the group consisting of ethyleneurea, propyleneurea, and1,3-dimethylurea.
 16. A blocked hardener composition according to claim14, wherein an amine compound of the ureidoamine is selected from thegroup consisting of primary monoamines, secondary monoamines, primarydiamines, secondary diamines.
 17. A blocked hardener compositionaccording to claim 14, wherein the ureidoamine is selected from thegroup consisting of Structures I and II:

in which R and R′ are any combination of alkyl groups containing one totwelve carbon atoms; or R is any combination of an alkyl groupcontaining from one to twelve carbon atoms and R′ is benzyl; or R ismethyl or ethyl and R′ is anilino-, or R is methyl and R′ is2-hydroxyethyl-, or R and R′ are both 2-hydroxyethyl-, or R is methyland R′ is 2-hydroxyisopropyl-, or R and R′ are both 2-hydroxyisopropyl-;or R and R′ are both 3-dimethylaminopropyl-; or RR′N— is the iminoradical bis(dimethylamino)methaneimino- derived fromtetramethylguanidine, or RR′N— is heterocyclic and selected frompiperidyl-, 4-methylpiperidyl-, pyrrolidyl-, 1-methylpiperazinyl-,1-imidazolyl-, 1-(2-methyl)imidazolyl-, 1-(2-ethyl)imidazolyl-,1-(2-ethyl-4-methyl)imidazolyl-, or 1-benzimidazolyl-.
 18. A blockedhardener composition according to claim 14, wherein the ureidoamine isStructure III:


19. A blocked hardener composition according to claim 14, wherein theureidoamine is selected from the group consisting of Structures IVa,IVb, V, and VI:

wherein R is an alkyl containing from 1 to 12 carbon atoms, allyl-,benzyl-, 2-hydroxyethyl-, 2-hydroxyisopropyl-, 3-hydroxy-1-propyl-,3-ethoxypropyl-, 3-propoxypropyl-, 3-isopropoxypropyl-,2-(2-hydroxyethoxy)ethyl-, 3-(dimethylamino)propyl-,3-(diethylamino)propyl-, or 3-(1-imidazolyl)propyl-; or RN═ is aheterocyclic group in which R represents cyclohexyl-;3-(pyridyl)methyl-; 2-pyridyl-; 2,4-diethyl-N-anilino-;2,6-diethyl-N-anilino-; or 2-pyrimidyl-.
 20. A blocked hardenercomposition according to claim 19, wherein the ureidoamine is anoligomer of Structure VI selected from the group consisting ofStructures VIa and VIb:


21. A blocked hardener composition according to claim 14, wherein theureidoamine is Structure VII;

X is ethylene; and R is CH₂CH₂OH or CH₂CH₂NH₂.
 22. A blocked hardenercomposition according to claim 14, wherein the ureidoamine is selectedfrom the group consisting of Structures VIII and X:

wherein X is ethylene, polyoxypropylene, hexamethylene, cycloaliphatic,or aromatic.
 23. A blocked hardener composition according to claim 14,wherein the ureidoamine is Structure IX:

wherein x is ethylene, polyoxypropylene, hexamethylene, cycloaliphatic,or aromatic; and R and R′ are alkyl groups containing 1-12 carbon atoms,or R is an alkyl group containing 1-12 carbon atoms and R′ is benzyl, Ris methyl or ethyl and R′ is anilino-, or R is methyl and R′ is2-hydroxyethyl-, or R and R′ are both 2-hydroxyethyl-, or R is methyland R′ is 2-hydroxyisopropyl-, or R and R′ are both 2-hydroxyisopropyl-;or R and R′ are both 3-dimethylaminopropyl-; or RR′N— represents theimino radical bis(dimethylamino)methaneimino-, or RR′N— is heterocyclic,in which case RR′N— is piperidyl-,4methylpiperidyl-, pyrrolidyl-,1-methylpiperazinyl-, 1-imidazolyl-, 1-(2-methyl)imidazolyl-,1-(2-ethyl)imidazolyl-, 1-(2-ethyl-4-methyl)imidazolyl-, or1-benzimidazolyl-.
 24. A blocked hardener composition according to claim14, wherein the ureidoamine derivative is an acyl derivative ofStructure VI:

wherein R— is dialkylaminopropyl- or imidazolylpropyl- and the acylcompound is one of 2,2-bis(hydroxymethyl)propionicacid;2,2-bis(hydroxymethyl)butyricacid or glycolicacid.
 25. A blockedhardener composition according to claim 14, wherein the ureidoaminederivative is an acyl derivative of Structure IVa:

wherein R— is dialkylaminopropyl- or imidazolylpropyl- and the acylcompound is one of 2,2-bis(hydroxymethyl)propionicacid;2,2-bis-(hydroxymethyl)butyricacid or glycolicacid.